1. Field of the Invention
The present invention relates to a toque based monitor of detected output torque of the powertrain of a Hybrid Electric Vehicle (xe2x80x9cHEVxe2x80x9d) and compares it to a desired output torque of the operator.
2. Discussion of the Prior Act
The need to reduce fossil fuel consumption and pollutants from automobiles and other vehicles powered by an internal combustion engines (ICE""s) is well known. Vehicles powered by electric motors have attempted to address these needs. However, electric vehicles have limited range and limited power coupled with the substantial time needed to recharge their batteries. An alternative solution is to combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called hybrid electric vehicles (HEV""s). See generally, U.S. Pat. No. 5,343,970 (Severinsky).
The HEV has been described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. A series hybrid electric vehicle (SHEV) is a vehicle with an engine (most typically an ICE) which powers a generator. The generator, in turn, provides electricity for a battery and motor coupled to the drive wheels of the vehicle. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) is a vehicle with an engine (most typically an ICE), battery, and electric motor combined to provide torque to power the wheels of the vehicle.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both the PHEV and the SHEV. The PSHEV is also known as a torque (or power) splitting powertrain configuration. Here, the torque output of the engine is given in part to the drive wheels and in part to an electrical generator. The generator powers a battery and motor that also provide torque output. In this configuration, torque output can come from either source or both simultaneously. The vehicle braking system can even deliver torque to drive the generator to produce charge to the battery.
The desirability of combining the ICE with an electric motor is clear. The ICE""s fuel consumption and pollutants are reduced with no appreciable loss of performance or range of the vehicle. Nevertheless, there remains substantial room for development of ways to optimize these HEV""s operational parameters.
One such area of HEV development is throttle control mechanisms. In prior art throttle controls, a direct physical link (an accelerator cable) between an accelerator pedal (pedal) and a throttle body controls a throttle plate of the ICE. The throttle plate is pulled open by the accelerator cable as the driver depresses the pedal. This increases engine speed and torque. Although simple and dependable, this throttle control method is unable to adapt fuel consumption efficiency to changing traveling conditions.
An electronic throttle control (ETC) is a recent development for improving throttle control and efficient introduction of fuel air mixtures into an engine""s cylinders. With the ETC system, the accelerator pedal is no longer mechanically connected to the throttle body. Instead, an actuator positions the throttle plate by a system, process, or apparatus called a powertrain control module (PCM). The PCM determines the desired throttle position based on the accelerator pedal""s position sensor. This simple ETC system essentially mimics the conventional mechanical throttle and is often called the xe2x80x9cpedal followerxe2x80x9d ETC system.
To protect vehicle occupants, ETC systems soon added a second independent processor to detect ETC system failures. This processor determines if the system is in a safe mode of operation. If it is not in safe mode, vehicle operation is restricted and throttle plate control is prohibited.
Ford""s second generation ETC (2GETC) systems have added greater vehicle control. These systems no longer control in the xe2x80x9cpedal followerxe2x80x9d mode, but in a xe2x80x9ctorque controlxe2x80x9d mode. Accelerator position, vehicle speed, and barometric pressure in torque control mode are mapped into a desired/demanded driver torque request/wheel torque request. In torque control mode, the PCM can independently control vehicle subsystems such as throttle plate position, transmission gear, transmission slip, ignition timing, and fuel delivery to provide the desired wheel torque. To improve vehicle efficiency, torque control monitor systems add a monitoring scheme to ensure powertrain torque output is not greater than the demanded torque output. See generally, U.S. Pat. No. 5,673,668 to Pallett, et. al. (Ford Global Technologies, Inc.).
Unfortunately, the 2GETC engine torque output comparison is no longer sufficient for HEV. The HEV also has an electric traction drive motor and generator adding torque to the vehicle""s powertrain. The ETC for the HEV must establish control of the HEV""s entire powertrain. HEV patents that reference ETC""s are described in U.S. Pat. No. 5,656,921 to Farrall and U.S. Pat. No. 5,806,617 to Yamaguchi. Yet no one has ever adapted the 2GETC to the HEV.
The present invention adapts the second generation ETC (2GETC) systems xe2x80x9ctorque control modexe2x80x9d for an HEV and monitors net output shaft torque and regenerative braking to determine torque demand.
More specifically, the monitor""s independent plausibility check (IPC) independently determines the driver""s request for output shaft torque of the entire powertrain. This request includes a contribution from the brake control unit to achieve regenerative braking information from the powertrain""s electric traction motor and generator. The IPC determines whether the detected torque exceeds the desired torque and mitigates or shuts down torque delivered if necessary. These detection and mitigation (or limiting) systems are key features of this invention.
The monitor""s IPC independently estimates output shaft torque during all modes of operation from all sources of torque including: the engine, generator, and motor. For example, the IPC estimates engine torque by using 2 methods, relative throttle position (TP_REL) and mass air flow (MAF). Likewise, the IPC estimates torque produced or absorbed by the motor and generator by comparing a transaxle management unit (TMU) supplied value and with a redundant sensor set. The IPC will also determine inertia torque from the engine and generator components for the transient torque during engine start-up and stop operation.